This invention relates to a method and apparatus for recovering or interpolating image information. In particular, the invention pertains to a method and apparatus for estimating the true color of each pixel of an image acquired by a detector with an arbitrary repeating pattern of detectors having different spectral sensitivities. The invention also relates to a method and apparatus for evaluating various detector configurations and for calibrating the response of such detectors.
In an imaging system employing a detector array having individual detector elements defining pixels, it is necessary to divide the detector into different wavelength response bands. This is achieved by rendering selected pixels sensitive to different wavelengths by means of filter elements. Typically, this is conventionally accomplished by locating the various filter elements over selected pixels in a pattern. The resulting structure, shown in FIG. 1, reveals a detector 10 having an active area divided into an array of individual detectors 12 each of which has a filter of a selected bandwidth over it. In the example illustrated in FIG. 1, three filters 14, 16 and 18 having band widths corresponding, for example, to red (R), green (G) and blue (B), respectively, are disposed over selected detectors 12 in an arbitrary pattern. In the example, the pattern is a repeating pattern of RGB in each row: RGBRGB . . . and in each column: RGBRGB . . . but offset one pixel per row as shown.
Unfortunately, filtering each detector for a selected bandwidth results in lost information at each pixel in the nonselected bands, i.e. the red filter 14 eliminates the green and blue information for the detector 12 with which it is associated. Thus, the information is lost. The same is true for the respective green and blue filters 16 and 18 with respect to the other bands.
It is desirable to recover the lost information so that the image to be detected is as close as possible to the real image scene.
It is not a simple matter to recover the lost data or to calibrate or to predict the true color content of a filtered detector. In addition, known recovery methods do not allow for the ready manipulation of detector patterns for different applications nor are they optimal in terms of minimizing the RMS error between the received image and the actual scene.
Accordingly, a method and apparatus for optimally recovering or interpolating missing image data in a detector array is desirable. It is also desirable to be able to evaluate different detector patterns. In accordance with the invention, computation of recovery coefficients is equivalent to calibration of the detector and the mosaic.